From: "Robin H. Johnson" <robbat2@gentoo.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
"Robin H. Johnson" <robbat2@gentoo.org>,
linux-kernel@vger.kernel.org, mingo@redhat.com,
rjohnson@digitalocean.com,
Arnaldo Carvalho de Melo <acme@kernel.org>
Subject: Re: [PATCH 1/2] tracing: show size of requested buffer
Date: Thu, 7 Oct 2021 17:26:04 +0000 [thread overview]
Message-ID: <robbat2-20211007T172058-955036195Z@orbis-terrarum.net> (raw)
In-Reply-To: <20211007092358.65152792@gandalf.local.home>
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On Thu, Oct 07, 2021 at 09:23:58AM -0400, Steven Rostedt wrote:
> On Thu, 7 Oct 2021 09:11:51 +0200
> Peter Zijlstra <peterz@infradead.org> wrote:
>
> > > > +++ b/kernel/trace/trace_event_perf.c
> > > > @@ -400,7 +400,8 @@ void *perf_trace_buf_alloc(int size, struct pt_regs **regs, int *rctxp)
> > > > BUILD_BUG_ON(PERF_MAX_TRACE_SIZE % sizeof(unsigned long));
> > > >
> > > > if (WARN_ONCE(size > PERF_MAX_TRACE_SIZE,
> > > > - "perf buffer not large enough"))
> > > > + "perf buffer not large enough, wanted %d, have %d",
> > > > + size, PERF_MAX_TRACE_SIZE))
> >
> > Priting a constant seems daft.. why is any of this important in any way?
>
> I see your point, but it can be useful if you changed it, and want to know
> if you are running the kernel with the change or not.
>
> I've done daft things were I changed a const and was running a kernel
> without the change and couldn't understand why it wasn't working ;-)
Yes, my initial internal versions of this series only bumped the
constant, and then I was running a few different kernels, and being able
to compare which value was in use became a problem.
I was trying to think further what would make sense for the constant.
- What are the negative impacts of a too-large value?
- Is there demand for more reconfigurability?
- Should PERF_MAX_TRACE_SIZE be a knob in Kconfig?
--
Robin Hugh Johnson
Gentoo Linux: Dev, Infra Lead, Foundation Treasurer
E-Mail : robbat2@gentoo.org
GnuPG FP : 11ACBA4F 4778E3F6 E4EDF38E B27B944E 34884E85
GnuPG FP : 7D0B3CEB E9B85B1F 825BCECF EE05E6F6 A48F6136
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next prev parent reply other threads:[~2021-10-07 17:26 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-31 4:37 [PATCH 1/2] tracing: show size of requested buffer Robin H. Johnson
2021-08-31 4:37 ` [PATCH 2/2] tracing: increase PERF_MAX_TRACE_SIZE to handle Sentinel1 and docker together Robin H. Johnson
2021-09-08 1:24 ` [PATCH 1/2] tracing: show size of requested buffer Steven Rostedt
2021-10-07 7:11 ` Peter Zijlstra
2021-10-07 13:23 ` Steven Rostedt
2021-10-07 17:26 ` Robin H. Johnson [this message]
2021-10-08 22:13 ` Steven Rostedt
2021-10-09 0:21 ` Robin H. Johnson
2021-10-26 20:43 ` Steven Rostedt
2021-10-26 21:23 ` Peter Zijlstra
2021-10-26 21:26 ` Steven Rostedt
2021-10-06 22:26 ` Steven Rostedt
2021-10-06 22:48 ` Robin H. Johnson
2021-10-07 0:55 ` Steven Rostedt
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